In the development and application of the space-air-ground integrated network (SAGIN), the intricate network structure and varied resources significantly affect the service capabilities of SAGIN. It is a challenge in the popularization of SAGIN to allocate and optimize resources to improve the performance in heterogeneous networks. Firstly, the architecture and functions of SAGIN were introduced. Subsequently, several typical issues in resource optimization were summarized and analyzed, along with the common performance objectives, modeling and optimization methods. Finally, the challenges in network optimization were analyzed, and the future research direction in this field was discussed
